1. Field of the Invention
The present invention relates to a semiconductor substrate, a substrate for semiconductor crystal growth, a semiconductor device, an optical semiconductor device, and manufacturing methods thereof.
2. Description of the Related Art
A semiconductor device using a nitride semiconductor is used as a power device operating at a high frequency and high output. In the semiconductor device, a sapphire substrate or the like is used as a growth substrate of a semiconductor crystal layer. However, there is a large difference between the lattice constant and the thermal expansion coefficient of the growth substrate and the lattice constant and the thermal expansion coefficient of the semiconductor crystal layer. Thereby, there have been risks that, for example, the whole semiconductor device is warped, cracks are generated, leading to lowering of the yield ratio.
Therefore, a technique to provide a stress offsetting layer on the rear side of the growth substrate has been disclosed (for example, refer to Japanese Patent Application Publication No. 2003-113000). According to the technique, it is possible to inhibit warp of the growth substrate and generation of cracks by the stress offsetting layer.
However, the inventors of the present invention have found that it is not possible to effectively inhibit peeling at the interface between the growth substrate and the semiconductor crystal layer, or peeling at the interface between respective semiconductor layers in the growth substrate and the semiconductor crystal layer by the foregoing technique disclosed in Japanese Patent Application Publication No. 2003-113000.